[-cxx-abi microsoft] Emit linkonce_odr definitions for declarations of static...

[-cxx-abi microsoft] Emit linkonce_odr definitions for declarations of static data members with inline initializers (PR17689)

This makes Clang emit a linkonce_odr definition for 'val' in the code below,
to be compatible with MSVC-compiled code:

  struct Foo {
    static const int val = 1;
  };

Differential Revision: http://llvm-reviews.chandlerc.com/D2233

llvm-svn: 195283